1. Field of the Invention
The present invention relates to a water quality control method and device for a nuclear plant, and a nuclear power plant and, in particular, relates to a water quality control method and device for a water cooling direct cycle type nuclear power plant which is suitable for further reducing concentration of radioactive corrosion products in the reactor water, in other words a nuclear power plant including such a nuclear reactor as a boiling water reactor and an advanced converter reactor wherein water is used as a coolant, and further relates to a water cooling direct cycle type nuclear power plant.
2. Description of Related Art
JP-A-61-79194 (1986) discloses a conventional method of controlling concentration of corrosion products in the feed water wherein .sup.58 Co ion concentration in the reactor water is reduced by adjusting Fe/Ni concentration in the feed water from 2 to 10.
Further, JP-A-1-316692 (1989), which corresponds to U.S. Pat. No. 5,015,436, discloses to reduce .sup.60 Co ion concentration in the reactor water by controlling iron concentration in the feed water by making use of the iron accumulation rate on fuel rod surfaces as a control index.
The former conventional method only notes the Fe/Ni concentration ratio in the feed water for achieving an optimum control, however even when .sup.58 Co ion concentration of a low level is achieved while fulfilling a required condition of the Fe/Ni concentration ratio, .sup.60 Co ion concentration in the reactor water possibly increases beyond an estimated level, therefore the use of the Fe/Ni concentration ratio as a control index leaves a problem.
The latter conventional method which controls the iron concentration by making use of the ion accumulation rate on the fuel rod surfaces as a control index resolves the problem in the former conventional method, however when a hydrogen injecting operation is performed for such as counter-measuring a stress corrosion cracking of reactor structures, the reactor water environment changes into a reducing atmosphere and dissolution of oxides is accelerated, as a result, an eluting speed of .sup.60 Co ion from oxide layers of Co accumulated on the fuel rod surfaces is increased, therefore .sup.60 Co ion concentration in the reactor water is presumed to increase again.
Further, in view of an effective use of fuels there is a plan to prolong the life time of fuels, in other words prolonging one operating cycle period, and to increase burn-up of the fuels. The greater output extraction from the fuels according to the plan leads to quickening of radio activation of Co deposited on the fuel rod surfaces and to increasing radio activity ratio. Accordingly, in response thereto an increase of .sup.60 Co ion concentration in the reactor water is presumed.
However, in conventional nuclear power plant control no sufficient considerations are given for the problems which will be caused in association with changes in operation environment in future such as the hydrogen injecting operation and the increase of burn-up of the fuels.